Method of and apparatus for making high pressure tube bends, especially for the chemical industry

ABSTRACT

Method of and apparatus for producing tube bends for high pressure and high temperature use. A seamless tube is hot bent whereby to provide a semi-finished product, such semi-finished product is then filled with sand and tamped it in place. The method then proceeds with closing the ends of the thus sandfilled semi-finished product with lids, again heating the thus prepared semi-finished product to bending temperature, and the thrusting the heated semi-finished product downwardly through a female die by an aligned male die, whereby to produce a tube bend of oval form the longer axis of which is parallel to the bending axis of the semi-finished product and has a length which is 3 to 4 percent longer than its shorter axis. Thereafter the covers and sand are removed from the product, and after again heating the thus formed product calibrating it so as to change the oval cross-section thereof into a section which is circular in crosssection.

United States Patent 1191 Maev et al.

[ 5] Nov. 18, 1975 i 1 METHOD OF AND APPARATUS FOR MAKING HIGH PRESSURETUBE BENDS, ESPECIALLY FOR THE CHEMICAL INDUSTRY [75] Inventors: RadkoMaev; Cestmir Zacek; Petr Janak; Jan Strecha, all of Brno; Josef Duzy;Ludek Lucak, both of Ostrava, all of Czechoslovakia [73] Assignee:Kralovopolska strojirna, narodni podnik, Bmo-Kralovo Pole,Czechoslovakia [22] Filed: Aug. 9, 1974 [21] Appl. No.: 496,121

3328996 7/l967 Pin et al 72/369 Primary E.\'aminer-Lowell A. LarsonABSTRACT Method of and apparatus for producing tube bends for highpressure and high temperature use. A seamless tube is hot bent wherebyto provide a semi-finished product, such semi-finished product is thenfilled with sand and tamped it in place. The method then proceeds withclosing the ends of the thus sand-filled semi-finished product withlids, again heating the thus prepared semi-finished product to bendingtempera' ture, and the thrusting the heated semi-finished productdownwardly through a female die by an aligned male die, whereby toproduce a tube bend of oval form the longer axis of which is parallel tothe bending axis of the semi-finished product and has a length which is3 to 4 percent longer than its shorter axis.

Thereafter the covers and sand are removed from the product, and afteragain heating the thus formed prod uct calibrating it so as to changethe oval cross-section thereof into a section which is circular incrosssection.

3 Claims, 2 Drawing Figures US. Patent Nov. 18, 1975 METHOD OF ANDAPPARATUS FOR MAKING HIGH PRESSURE TUBE BENDS, ESPECIALLY FOR THECHEMICAL INDUSTRY This invention relates to the production of tube bendsor elbows, which are adapted for use under high pressure and/or hightemperatures, by forming them from straight seamless tubes of carbon oralloy steels. Such tube bends are employed in very substantialquantitles in the chemical industry.

Tube bends of this kind are presently manufactured from forged pieces intube form or from rolled seamless tubes, the processing of which is doneeccentrically with a consequent strength decrease of the bending zone ofthe outer wall of the bends caused by the bending process. The tube istamped full of sand and is then bent by a bending machine or in a presswith assistance of different tools. The eccentric tube working is,however, severe and costly; such bending often causes the cross-sectionof the passage through the elbow to be narrowed, thus causing anirregular weakness of the wall and an undesirable oval shape, thebending radius and the distance between the tube ends beingunpredictable.

The above mentioned disadvantages of the prior art methods and apparatusfor making tube bends are overcome by the method of and apparatus formanu facturing tube elbows in accordance with the invention.

A particular object of the invention is the provision of a method ofproducing elbows from straight seamless tubes, from which asemi-finished product is made by hot-bending the cross-section of whichat the same time receives an oval shape, the longer axis of the ovalsemifinished product, which is parallel to thebending axis, being 3 to 4percent longer than the shorter axis. The semi-finished product is thentamped full with sand, both ends of the product are closed with suitablecovers, and after being heated to the desired bending temperature, isbent while keeping its oval shaped crosssection. At the end of suchbending, the covers are removed from the ends of the product and thesand is removed therefrom. The elbow is again heated and is calibratedby being worked between shaped dies having a cavity of the desired shapeformed between them, such calibration further deforming the metal of thetube bend so that its cross-section and the cross-section of the passagetherethrough are made circular.

The invention also includes the apparatus for carrying out the abovemethod, such apparatus including a rod or mandrel which has a straightportion of circular cross-section at the entering end thereof, the otherend of the rod being in the form of a hood of oval cross-section havingits longer axis parallel to the bending axis of the semi-finishedproduct and 3 4 percent longer than its shorter axis. A section ofstraight seamless tube is telescoped over the entering, straightcircular portion of the rod after being heated to a suitable heatingtemperature and it is thrust down the length of the rod and around thehook thereon so as to form a curved, semifinished product with a radiusof bending somewhat greater than that desired in the finished product,and with the passage through the semi-finished form of oval shapedcorresponding to the shape of the cross section of the hook or themandrel.

The above-referred to apparatus further comprises a female die withrounded workpiece-engaging surfaces, the shortest distance between whichis the sum of a distance from a mid-axis of the semi-finished piece andthe opposite outer surfaces thereof. The apparatus further comprises amale die or presser element by which the semi-finished product is thrustthrough the female die in engagement with the working surfaces thereof,the center line of the passage through the workpiece then lying at equaldistances between the opposed surfaces of the elbow cross-section. Theworking surfaces of the female die and the working surfaces of thepressure element are formed in such manner that upon thrusting the piecethrough the female die the workpiece is formed to be oval incross-section with its longer axis parallel to the bending axis of theelbow and 3 to 4 percent longer than the shorter axis thereof.

The invention has among its objects the provision of an apparatus whichhas the capability of making high pressure tube bends from straightseamless tubes. It permits bends to be made with relatively small andsimple apparatus, such tube bends having walls of high strength and apassage of circular cross-section.

In the drawing attached hereto there is shown an example of theapparatus of the invention in shcematic form.

In the Drawings:

FIG. 1 is a view in longitudinal section through a first part of suchapparatus, the apparatus being shown after it has formed a seamless tubesection into an intermediate or semi-finished tube bend product; and

FIG. 2 is a view in vertical section of female and male dies for furtherbending the intermediate product shown in FIG. 1 so as to reduce theradius of bending of such product.

The apparatus of FIG. 1 consists of a rod or mandrel 1 in circularcross-section, on one end of which there is affixed a fixed lock 2. Onits other end rod 1 it has the form of a hook 3, which, as can be seenfrom FIG. 1, is bent to a circular form which the semi-finished product4 is to take. The hook 3 is furthermore so formed that it graduallychanges from a circular cross-section at its entering end to anoval-shaped cross-section at its mid and exit portions, the longer axisof the cross-section of the semi-finished product 4 being parallel tothe bending axis and 3 to 4 percent longer than the shorter axis of suchcross-section.

On rod 1 there exists a pressure part 5, which is moved by an apparatus(not shown) in the direction of the arrow. On rod 1 there are affixedseveral straight seamless tubes 6; rod 1 with the serially disposedtubes are led through a heating oven, not shown in the drawings. Thetube bends 4 are discharged from the bending mandrel after passing end 3thereof.

FIG. 2 shows the clearly recognizable semi-finished product 4, which istamped full with sand, and sealed by covers 7 on both ends and is putinto the female die 8 on a frame 9. Above die 8 there is situated apressure element 10. In the frame 9 below die 8 there is illustrated anelbow 11, which already has attained the necessary bending radius.

The rounded working surfaces 12 of the female die 8 are so designed,that the smallest distance between them are equal to the elbow middleline distance (11 respectively 13) and to the elbow cross-sectionaldiameter.

Furthermore, the working surfaces 12 of the female die 8 and the workingsurfaces 14 of the pressure element 10 are formed in such a way thatwhile lowering the pressure element 10 into the female die 8 each hollowspace created shows a transverse oval cross-sea 3 tion, the longer axisof which is parallel to the elbowbending axis and is 3 to 4 percentlonger than its shorter axis.

The method of production and the function of the apparatus are asfollows:

Onto the rod 1, which first has to be unclamped from lock 2 and removedfrom pressure part 5, a number of tubes 6 are affixed, whereby they arepushed through the pressure part after mandrel 1 has again been affixedto lock 2. Now the heating oven is turned on. As soon as the temperaturehas reached the necessary temperature, the pressure part 5 is thrust tothe left. Pressure is being applied to the front part of the tube 6,which is then transferred over to the hook 3, whereby the tube is guidedalong the hook 3 and through continuous heating is bent and formed insuch a way that the semi-finished product 4 is created, product 4 havingan oval-shaped cross-section.

Thereafter the semi-finished product 4 is filled with sand, closed onboth ends with covers 7, heated in an oven, and put into the female die8. By means of the pressure element 10 pressure is applied to thesemi-finished product 4, whereby the rounded working surfaces 12 of thefemale die 8 and the working surfaces 14 of the pressure element deformthe semi-finished product 4 in such a way that the bending radius isdecreased in the desired way and an elbow 11 is created with an ovalcross-section.

Finally, after removal of covers 7 and, respectively, sand and afterrenewed heating, elbow 11 is calibrated by being formed again in ahydraulic press with the application of a calibration-apparatus. Suchcalibration hollow space determins the final form of the finished elbow,which cross-section is circular. In such calibration the outer wall ofthe elbow, which has experienced a decrease in strength in its bendingzone due to the formation conducted in the female die 8, is thickenedwithout renewed sand filling and tamping.

Although the invention is illustrated and described with reference toone preferred embodiment thereof, it is to be expressly understood thatit is in no way limited to the disclosure of such a preferredembodiment, but is capable of numerous modifications within the scope ofthe appended claims.

What is claimed is:

1. Method of producing tube bends for high pressure and high temperatureuse, comprising hot bending a seamless tube whereby to provide asemi-finished generally U-shaped product having legs disposed angularlywith respect to each other, filling such semi-finished product with sandand tamping it in place, closing the ends of the thus sand-filledsemi-finished product with lids, again heating the thus preparedsemi-finished product to bending temperature, and then thrusting theheated semi-finished product downwardly through a female die by analigned male die, whereby to reduce the angle between the legs of theproduct and to produce a tube bend of oval form the longer axis of whichis parallel to the bending axis of the semi-finished product and has alength which is 3 to 4 percent longer than its shorter axis, thereafterremoving the covers from the product and the sand from within it and,after again heating the thus formed product, calibrating it so as tochange the oval cross-section thereof into a section which is circularin cross-section.

2. Apparatus for producing tube bends for high pressure and hightemperature use, comprising a mandrel with a bent hook-shaped end and astraight portion leading to such hook shape end, means for attaching theend of the straight portion of the mandrel to a fixed support, atube-thrusting element which is telescoped over the straight end portionof the mandrel after a seamless tube has been telescoped over themandrel, and means to thrust the tube-thrusting member to force the tubeinto engagement with and along the curved end portion of the mandrel,the straight portion of the mandrel being circular in cross-section, thetube entering end of the curved portion thereof changing gradually incross-section from circular to oval, the long axis of such ovalcross-section. being parallel to the bending axis and from 3 to 4percent longer than the shorter axis thereof.

3. Apparatus for producing tube bends for high pressure and hightemperature use, comprising a female die with opposed rounded workingsurfaces, the smallest distance between the opposed working surfaces ofthe die being equal to the distance between the outer side surfaces ofparallel confronting portions of a still further finished tube bend, anda male die for thrusting the semi-finished product through the femaledie, the male die having working surfaces with an outer rounded portionand two spaced parallel longitudinal portions, the distance between thespaced longitudinal portions of the male die being equal to the desireddistance between the inner confronting surfaces of the straight portionsof the still further finished tube bend product, the working surfaces ofthe female die and the working surfaces of the male die being formed insuch manner that the tube bend product which has been forced through thefemale die by the male die is of oval crosssection, such cross-sectionhaving its longer axis parallel to the bending axis of the tube bend andfrom 3 to 4 percent longer than its shorter axis.

1. Method of producing tube bends for high pressure and high temperatureuse, comprising hot bending a seamless tube whereby to provide asemi-finished generally U-shaped product having legs disposed angularlywith respect to each other, filling such semifinished product with sandand tamping it in place, closing the ends of the thus sand-filledsemi-finished product with lids, again heating the thus preparedsemi-finished product to bending temperature, and then thrusting theheated semi-finished product downwardly through a female die by analigned male die, whereby to reduce the angle between the legs of theproduct and to produce a tube bend of oval form the longer axis of whichis parallel to the bending axis of the semi-finished product and has alength which is 3 to 4 percent longer than its shorter axis, thereafterremoving the covers from the product and the sand from within it and,after again heating the thus formed product, calibrating it so as tochange the oval cross-section thereof into a section which is circularin cross-section.
 2. Apparatus for producing tube bends for highpressure and high temperature use, comprising a mandrel with a benthook-shaped end and a straight portion leading to such Hook shape end,means for attaching the end of the straight portion of the mandrel to afixed support, a tube-thrusting element which is telescoped over thestraight end portion of the mandrel after a seamless tube has beentelescoped over the mandrel, and means to thrust the tube-thrustingmember to force the tube into engagement with and along the curved endportion of the mandrel, the straight portion of the mandrel beingcircular in cross-section, the tube entering end of the curved portionthereof changing gradually in cross-section from circular to oval, thelong axis of such oval cross-section being parallel to the bending axisand from 3 to 4 percent longer than the shorter axis thereof. 3.Apparatus for producing tube bends for high pressure and hightemperature use, comprising a female die with opposed rounded workingsurfaces, the smallest distance between the opposed working surfaces ofthe die being equal to the distance between the outer side surfaces ofparallel confronting portions of a still further finished tube bend, anda male die for thrusting the semi-finished product through the femaledie, the male die having working surfaces with an outer rounded portionand two spaced parallel longitudinal portions, the distance between thespaced longitudinal portions of the male die being equal to the desireddistance between the inner confronting surfaces of the straight portionsof the still further finished tube bend product, the working surfaces ofthe female die and the working surfaces of the male die being formed insuch manner that the tube bend product which has been forced through thefemale die by the male die is of oval cross-section, such cross-sectionhaving its longer axis parallel to the bending axis of the tube bend andfrom 3 to 4 percent longer than its shorter axis.